Saltatory Conduction: Faster Impulse in Myelinated Fibres
Biology · Neural Control and Coordination · NEET
Saltatory conduction is the way a nerve impulse travels in a myelinated axon: the impulse "jumps" from one node of Ranvier to the next, instead of moving smoothly along the whole membrane. Because the myelin sheath insulates the axon and only the nodes get depolarised, the impulse is much faster than in an unmyelinated fibre. Memory hook: "saltare" means "to jump" in Latin, so picture the signal leaping between gaps in the myelin.
In a myelinated axon the impulse is regenerated only at the nodes of Ranvier (red) and jumps across the insulated myelin segments, so it travels faster than the smooth continuous conduction seen in unmyelinated fibres.
Your doubts, answered
Why is saltatory conduction faster than conduction in an unmyelinated axon?
In an unmyelinated axon the impulse must depolarise every tiny patch of membrane one after another, which is slow. In a myelinated axon the myelin sheath acts as an insulator, so ions cannot cross except at the nodes of Ranvier. The action potential is regenerated only at the nodes, so it effectively jumps from node to node and covers the same distance in much less time.
What exactly does the impulse jump between?
It jumps between nodes of Ranvier. These are the small gaps between two adjacent myelin sheaths where the axon membrane is exposed. Only at these gaps can Na+ enter and a fresh action potential form, so the signal appears to leap from one node to the next.
Does saltatory conduction happen in unmyelinated fibres?
No. Saltatory conduction needs myelin and nodes of Ranvier. Unmyelinated fibres have no insulating myelin sheath, so the impulse moves as a smooth, continuous wave along the whole membrane. This is called continuous conduction and it is slower.
Why does NCERT not use the word 'saltatory' but this concept is still important?
The NCERT chapter describes myelinated fibres with Schwann cells forming the myelin sheath and gaps called nodes of Ranvier. The term 'saltatory conduction' is the standard name for the jumping mechanism that these structures make possible, and NEET expects you to connect the structure (myelin + nodes) to the faster impulse.
What forms the myelin sheath that makes saltatory conduction possible?
Schwann cells wrap around the axon to form the myelin sheath in the peripheral nervous system. Myelinated fibres are found in spinal and cranial nerves. Where the sheath is interrupted, the nodes of Ranvier remain, and these are the sites where the impulse is regenerated during saltatory conduction.
⚠️ The NEET trap ✗ The impulse jumps across the myelin sheath itself, so myelin is where the action potential forms. ✓ The impulse jumps between the nodes of Ranvier (the gaps). The action potential is regenerated only at the nodes, because myelin is an insulator and blocks ion flow across the covered regions. 🧠 Myelin insulates; nodes regenerate. Depolarisation happens at the exposed nodes, never under the myelin.
Real NEET questions
NEET 2017
Myelin sheath is produced by
A · Schwann Cells and Oligodendrocytes ✓
B · Astrocytes and Schwann Cells
C · Oligodendrocytes and Osteoclasts
D · Osteoclasts and Astrocytes
Solution: The myelin sheath that insulates a nerve fibre and makes saltatory conduction possible is formed by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system. Astrocytes support neurons but do not make myelin, and osteoclasts are bone cells. So the correct pair is Schwann cells and oligodendrocytes. This matters for saltatory conduction because it is this myelin, broken by nodes of Ranvier, that lets the impulse jump node to node.
Solved Neural Control and Coordination NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the jumping of a nerve impulse from one node of Ranvier to the next in a myelinated axon, which makes conduction faster.
Where does depolarisation occur in a myelinated axon?
Only at the nodes of Ranvier, because the myelin sheath between the nodes insulates the axon and stops ions from crossing there.
Which fibres show saltatory conduction?
Only myelinated fibres, such as those in spinal and cranial nerves. Unmyelinated fibres show slower continuous conduction.
Why is myelin called an insulator here?
Myelin is a fatty covering that stops ion movement across the axon membrane, so current is forced to flow to the next exposed node instead of leaking out along the way.
Is saltatory conduction directly in NCERT?
NCERT describes the myelin sheath, Schwann cells and nodes of Ranvier that make it happen. 'Saltatory conduction' is the accepted name for this jumping mechanism and is expected in NEET.
